1. Field of the Invention
The present invention relates to hydraulic control systems for clutches, especially for motor vehicles.
More particularly it relates to the receiver for such a control system.
2. Description of the Related Art
As is known, the receiver, which is also referred to as an actuator, of such a control system comprises two parts in cylinder-and-piston relationship, namely a first part or fixed part, for fastening the control means on a fixed structure such as the casing of a gearbox, and a second part, or moving part, which typically consists of a piston sliding axially and mounted inside a blind cavity which is defined by the fixed part, the latter being hollow.
This cavity is arranged to be pressurised and to be depressurised.
In this way, with the piston, a variable volume chamber is defined.
For this purpose, the fixed part includes a feed inlet connected to the cavity.
The control fluid may be gaseous, such as compressed air, or liquid, for example oil, the control system being generally referred to as a hydraulic control system.
The feed inlet is connected to the emitter of the control system through a duct. This emitter is actuated by the clutch pedal, or, in a known way, by an actuator which has for example an electric motor actuating the piston of the emitter through an interposed mechanical transmission.
The electric motor is governed by a computer which receives information from sensors, which are associated in particular with the gear change lever and with the driving and driven shafts, so as to measure the speed of rotation of these latter.
The fixed part of the receiver includes for example ears for fastening it on a fixed part such as the casing of the gearbox.
For more detail, reference should be made to the document WO96/24781.
In another version, the fixed part comprises at least one external body, a sole plate arranged to be fixed on the casing of the gearbox, and bayonet mounting means interposed between the external body and the sole plate, which is preferably of metal.
Thus, the external body may be standardised, while the sole plate serves as an adaptor and is configured according to the application, and more precisely as a function of the form of the fixed part on which it is fastened.
Such an assembly is described for example in the document FR-96 02591 filed on Feb. 26, 1996.
In those two documents, the cavity is defined by an external body of mouldable material, and by a concentric internal tube.
The components are arranged coaxially and concentrically.
The tube is of metal and constitutes a support and guiding member for the piston that actuates the clutch release bearing of the clutch.
For the best explanation, reference should be made to FIG. 1, which corresponds to FIG. 2 in the document WO-A-96/24781.
Thus, shown at 1 is a conventional clutch of the push-to-release type, in which the declutching device consists of the fingers of a diaphragm 13, on the inner ends of which there acts a clutch release bearing 3 which, in this case, is part of the receiver 2 of the hydraulic clutch control system.
In another version, the declutching device of the clutch may consist of declutching levers acting on springs which are mounted between the cover plate 14 and the pressure plate 12 of the clutch. Auxiliary springs may be provided. These springs may act in series, or in parallel with the diaphragm. A series arrangement is described for example in the document FR-97 11058 filed on Sep. 5, 1997, with the clutch being then able to be equipped with a wear compensating device to compensate for wear in the friction liners 16 of the disc 11.
In this Figure, by way of example, the diaphragm 13 is mounted for pivoting movement on the cover plate by means of short posts 20.
The diaphragm 13 acts on the pressure plate 12 through its Belleville ring portion, so as to grip the friction liners 16 of the friction wheel 11 between the pressure plate 12 and the reaction plate 10 of the clutch.
In the context of an application to a motor vehicle, the torque is thus transmitted from the crankshaft (not shown) of the engine of the vehicle, on which the reaction plate 10 is secured by means of screws, to the input shaft of the gearbox (not shown) on which the internally splined hub 17 of the friction wheel 11 is mounted.
The clutch is thus engaged, with the piston 4 being retracted by its maximum amount in the cavity 50 defined by the fixed body 5,6, which in this case is in two coaxial and concentric parts, namely the external body 5, of a casting material which is aluminium based for example, and the metallic internal tube 6 which is surrounded by the body 5.
The feed inlet is shown at 56 and is formed by moulding with the body 5, which in this case is of tubular form, while the duct coming from the emitter of the hydraulic control system is shown at 58.
This feed inlet 56 has an internal channel which is open in the base of the cavity 50, the piston 4 having at its rear end a seal 45 for sealing the cavity 50. The volume of the control chamber is then at a minimum value.
When the cavity 50 is pressurised with a control fluid from the above mentioned emitter via the duct 58 and the inlet 56, the piston 4 is caused to be displaced towards the left in FIG. 1, so that the volume of the control chamber is increased.
The diaphragm 13 pivots because of the short posts 20, so that its gripping action on the pressure plate 12 diminishes progressively.
At the end of a displacement C, or declutching travel, of the piston 4 and of the clutch release bearing 3, which in this case is carried by the piston 4, the diaphragm 13 no longer exerts any force on the pressure plate 12. Tangential tongues (not shown) then return the pressure plate towards the base of the cover plate 14, which in the present case is secured by means of screws, not shown, on the reaction plate 10.
The clutch is now disengaged; an axial clearance (not shown) exists between the friction liners 16 and the pressure plate 12. The torque is then no longer transmitted from the driving shaft (the crankshaft of the engine) to the driven shaft (the input shaft of the gearbox).
It will be recalled that the tangential tongues mentioned above provide coupling in rotation, with axial mobility, between the cover plate 14 and the pressure plate 12.
The volume of the control chamber is now at a maximum value, with the piston 4 occupying a deployed position (as in the upper part of FIG. 1).
When the cavity 50 is depressurised, the piston 4 returns, under the action of the diaphragm 13, to its initial retracted position (as in the lower part of FIG. 1).
The clutch release bearing defines the actuating element which acts in a thrust mode on the declutching device (i.e the diaphragm 13) of the clutch, and here it comprises a ball bearing, the rotating ring of which is in contact, permanently in this case, with the diaphragm 13 through a preloading spring 7 acting between the body 5 and the piston 4.
The spring 7 is protected by a bellows 8 surrounding the spring 7.
As can be seen, the internal tube 6 is longer in the axial dimension than the external body 5, and is of low thickness, which reduces overall radial size.
The body 5 has a thin tubular front portion for guiding the spring 7, and a thicker rear portion in the form of a collar.
The inlet 56 is connected to the collar portion, the front face of which serves as an abutment for the spring 7, the other end of which is in engagement on a transverse flange formed on the piston 4 at its front end. This transverse flange serves as the abutment for the nonrotating ring of the bearing 3, the bellows being attached to the said ring and gripped by a piece in contact with the front transverse face of the collar portion of the body 5.
A guide sleeve 9 carried by the tube 6 guides the tubular piston 4, as does the axially oriented cavity 50.
The presence of the sleeve 9 is of course not obligatory, as can be seen in the above mentioned document FR-96 02571, and the piston 4 can be of plastics material or include rings for its sliding motion along the tube 6.
In all cases, the tube 6 preferably carries a stop abutment, such as the sleeve 9 or a toroidal ring, for limiting the displacement of the piston 4.
It is possible to construct a sub-assembly in advance, because the tube has a generally transversely oriented flange at its rear end. This flange, which is annular, closes off the cavity 50 and defines the base of the latter.
The flange is in contact with a transverse abutment surface formed in the rear face of the collar portion of the external body 5 surrounding the internal tube 6.
A sealing ring is arranged at this level so as to seal the cavity 50.
The transverse abutment face defines a recess (a groove) at the rear of the body 5.
Thus, before the receiver 2 is mounted on the casing 21 of the gearbox, the spring 7 holds the flange of the metallic tube 6 in contact with the external body 5, which has ears, one of which can be seen at 51 in the lower part of FIG. 1, for fastening it to the casing of the gearbox, for example by means of screws.
The receiver 2 in this case is of the concentric type, because the input shaft of the gearbox passes through the internal tube 6. The recess is also defined by a surface for centring the flange of the tube, with the said part centring the said flange.
After the body 5 has been fixed on the casing 21, the flange of the internal tube 6 is clamped between the casing 21 and the rear face of the collar portion of the external body.
This arrangement makes it necessary to configure the casing 21 in such a way that the latter offers an abutment face to the flange of the internal tube 6.
Having regard to the form of the casing, this is not always possible.
In addition, it involves the need to respect precise tolerances between the casing and the rear of the external body, so that the flange will be properly clamped.
These tolerances take account of the fact that the external body is fixed on the casing either directly, for example by means of ears, or indirectly, with the aid of a sole plate for example.
An object of the present invention is to overcome these drawbacks in a simple and inexpensive way, but with strong retention of the flange in spite of variations in pressure in the cavity.